Method of determining target treatment locations

ABSTRACT

A method and system for automatic location of a target treatment structure, such as a pulmonary vein ostium, from an anatomical image. The method includes calculating a most likely path of blood flow through a pulmonary vein based on a cross-sectional area minimization technique and calculating pulmonary vein geometry as a function of length. For example, a pulmonary vein ostium may be located by analyzing a change in pulmonary vein dimensional size or other anatomical factors, such as absolute size. The method may also include determining tissue thickness at the pulmonary vein ostium or other treatment size for treatment dose optimization. The method may be an algorithm performed by a processing unit of a navigation system or other component of a medical system.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.15/259,744, filed Sep. 8, 2016, and entitled METHOD OF DETERMININGTARGET TREATMENT LOCATIONS, the entirety of which is incorporated hereinby reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

n/a

TECHNICAL FIELD

The present invention relates to a method and system for automaticallylocating target treatment sites, such as pulmonary vein ostia.

BACKGROUND

In many non-invasive or minimally invasive surgical and treatmentprocedures, navigating a medical device within a patient's body can bevery challenging. Navigation systems are frequently used to help theuser identify the location of the medical device and to steer themedical device to the target treatment location. For example, navigationis an important tool in many electrophysiological (EP) proceduresbecause it helps the user understand the placement of the medical devicewithin the cardiac space. Additionally, navigation is often used toplace medical devices at areas targeted for thermal treatment and/orablation.

When the medical device is a focal catheter, for instance, the ablatingsurface may be directly imaged on the navigation system and there is aclose, direct coupling between the navigation and the delivered therapy.However, other medical devices, such as balloon catheters, may have morecomplex geometry, and navigation electrodes on the device may notexactly correlate with the ablating surface (e.g., the surface of theballoon). Additionally, placement of these complex-geometry devices maybe difficult to infer from fluoroscopic imaging or navigation systemsrelative to the targeted tissue regions.

Ablation of the tissue surrounding one or more pulmonary veins, such asthe pulmonary vein ostium, has shown positive results in the treatmentof certain types of atrial fibrillation. The success of this treatment,however, largely depends on occlusion of the pulmonary vein with themedical device, which may be difficult to determine using currentimaging and navigation techniques, and delivery of the optimal treatmentdose, which may depend on tissue thickness at the treatment site,another complicating factor. Additionally, pre-procedural identificationof the ablation target sites and subsequent ablation tool selection(e.g., balloon catheter size) can facilitate faster and more predictableprocedures prior to invasive interaction with the patient.

SUMMARY

The present invention advantageously provides a method and system forlocating a target treatment site. In one embodiment, the system mayinclude a navigation system including a processing unit, the navigationsystem being configured to store an anatomical image of an area oftissue including the target treatment site, the processing having aprocessing circuitry with a memory and a processor, the memory incommunication with the processor and having instructions that, whenexecuted by the processor, configure the processor to: determine a firstcenter and an inner surface of an anatomical structure, the anatomicalstructure defining a lumen; determine a first plane that extends acrossa cross-sectional area of the anatomical structure; determine a firstvector that is normal to the first plane and extends from the firstcenter; determine a second vector that lies in the first plane, isnormal to the first vector, and extends from the first center; determinea first plurality of distances between the first center and the innersurface of the anatomical structure along the second vector around 2πradians around the first vector; determine a surface area of a firstarea defined by an intersection of the first plane and the inner surfaceof the anatomical structure, the surface area of the first area beingbased on the first plurality of distances; determine a second center ofthe anatomical structure, the second center being a predetermineddistance along the first vector from the first center; determine asecond plane that extends across a cross-sectional area of theanatomical structure, the second center being in the second plane;determine a third vector that is normal to the second plane and extendsfrom the second center; determine a fourth vector that lies in thesecond plane, is normal to the third vector, and extends from the secondcenter; determine a second plurality of distances between the secondcenter and the inner surface of the anatomical structure along the thirdvector around 2π radians around the first vector; determine a surfacearea of a second area defined by an intersection of the second plane andthe inner surface of the anatomical structure, the surface area of thesecond area being based on the second plurality of distances; andidentify a location of the target treatment site based on thedeterminations. In one embodiment, the processing may be furtherconfigured to: before determining the first plurality of distances,rotate the first vector in a first direction by a first amount to definea first adjustment plane and first adjustment vector; calculate asurface area of the first adjustment plane; rotate the first vector in afirst direction by a second amount to define a second adjustment planeand second adjustment vector; calculate a surface area of the secondadjustment plane; and select one of the first vector, the firstadjustment vector, and the second adjustment vector in which the surfacearea is minimized. In one embodiment, the processor may be furtherconfigured to: rotate the first vector in a second direction by a thirdamount to define a third adjustment plane and third adjustment vector;calculate a surface area of the third adjustment plane; rotate the firstvector in a second direction by a fourth amount to define a fourthadjustment plane and fourth adjustment vector; calculate a surface areaof the fourth adjustment plane; and select one of the first vector, thethird adjustment vector, and the fourth adjustment vector in which thesurface area is minimized. In one embodiment, the processor may befurther configured to determine an updated first plane and an updatedfirst vector based on the selected adjustment vectors. In oneembodiment, the processor may be further configured to determine anupdated first center based on the updated first plane, the firstplurality of distances being between the updated first center and theinner surface of the anatomical structure. In one embodiment, theprocessor may be further configured to determine a direction of bloodflow within the anatomical structure based at least in part on the firstand third vectors. In one embodiment, the processor may be furtherconfigured to determine a structure of the anatomical structure based atleast in part on the surface area of the first area and the surface areaof the second area. In one embodiment, the processor may be furtherconfigured to determine a direction of blood flow within the anatomicalstructure based on the first and third vectors. In one embodiment, theprocessor may be further configured to determine a structure of theanatomical structure based on the surface area of the first area and thesurface area of the second area. In one embodiment the anatomical imagemay be a segmented image and the segmented image may include an outersurface and an inner surface of the anatomical structure, and theprocessor may be further configured to determine a thickness of an areaof the anatomical structure between the outer surface and the innersurface. In one embodiment, the area of the anatomical structure is thetarget treatment site. In one embodiment, the anatomical structure is apulmonary vein and the target treatment site is an ostium of thepulmonary vein. In one embodiment, the system may further include amedical device including at least one treatment element and at least onemapping electrode, the at least one mapping electrode being incommunication with the navigation system. In one embodiment, thenavigation system may further include a display and at least onenavigation electrode. In one embodiment, the processor may be furtherconfigured to: determine a target position for the medical device; anddisplaying to the user the target position of the medical device on thenavigation system display.

In one embodiment, a system for locating a target treatment site mayinclude: a processing unit including a processing circuitry including amemory and a processor, the memory in communication with the processorand having instructions that, when executed by the processor, configurethe processor to: determine a plurality of planes, each of the pluralityof planes having a center and extending across a cross-sectional area ofan anatomical structure, the anatomical structure having a lumen and aninner surface, the plurality of planes being over a length of theanatomical structure; determine a plurality of vectors, each of theplurality of vectors extending from the center of a corresponding one ofthe plurality of planes; calculating a surface area of each of theplurality of planes, the surface area being bounded by the inner surfaceof the anatomical structure; calculating a difference between surfaceareas of each pair of adjacent planes of the plurality of planes;identifying a target treatment site based at least in part on thecalculated difference. In one embodiment the processor may be furtherconfigured to compare a direction of each of the plurality of vectors,the identification of the target treatment site being based at least inpart on the comparison. In one embodiment, the processing unit is partof a navigation system, the navigation system being configured to storean anatomical image of an area of tissue including the target treatmentsite, the determinations being based on the anatomical image. In oneembodiment, the anatomical image is a segmented image, the segmentedimage including an outer surface and an inner surface of the anatomicalstructure, the processor being further configured to: determine athickness of an area of the anatomical structure between the outersurface and the inner surface.

In one embodiment, a system for locating a target treatment site mayinclude: a navigation system including a processing unit, the navigationsystem being configured to store an anatomical image of an area oftissue including the target treatment site, the processing having aprocessing circuitry with a memory and a processor, the memory incommunication with the processor and having instructions that, whenexecuted by the processor, configure the processor to: determine a firstcenter and an inner surface of an anatomical structure, the anatomicalstructure defining a lumen; determine a first plane that extends acrossa cross-sectional area of the anatomical structure; determine a firstvector that is normal to the first plane and extends from the firstcenter; calculate a surface area of the first plane within an areabounded by the inner surface of the anatomical structure; determine asecond vector that lies in the first plane, is normal to the firstvector, and extends from the first center; rotate the first vector in apitch direction by a first amount to define a first adjustment plane andfirst adjustment vector; calculate a surface area of the firstadjustment plane within an area bounded by the inner surface of theanatomical structure; rotate the first vector in the pitch direction bya second amount to define a second adjustment plane and secondadjustment vector; calculate a surface area of the second adjustmentplane within an area bounded by the inner surface of the anatomicalstructure; select one of the first vector, the first adjustment vector,and the second adjustment vector in which the surface area is minimized;rotate the first vector in a yaw direction by a third amount to define athird adjustment plane and third adjustment vector; calculate a surfacearea of the third adjustment plane within an area bounded by the innersurface of the anatomical structure; rotate the first vector in the yawdirection by a fourth amount to define a fourth adjustment plane andfourth adjustment vector; calculate a surface area of the fourthadjustment plane within an area bounded by the inner surface of theanatomical structure; select one of the first vector, the thirdadjustment vector, and the fourth adjustment vector in which the surfacearea is minimized; determine an updated first plane and updated firstvector based on the selected one of the first vector, first adjustmentvector, second adjustment vector, third adjustment vector, and fourthadjustment vector; calculate a surface area of a first area defined byan intersection of the updated first plane and the inner surface of theanatomical structure, the surface area of the first area being based onthe first plurality of distances; determine a second center of theanatomical structure, the second center being a predetermined distancealong the first vector from the first center; determine a second planethat extends across a cross-sectional area of the anatomical structure,the second center being in the second plane; determine a third vectorthat is normal to the second plane and extends from the second center;determine a fourth vector that lies in the second plane, is normal tothe third vector, and extends from the second center; rotate the thirdvector in the pitch direction by the first amount to define a fifthadjustment plane and a fifth adjustment vector; calculate a surface areaof the fifth adjustment plane within an area bounded by the innersurface of the anatomical structure; rotate the third vector in thepitch direction by the second amount to define a sixth adjustment planeand a sixth adjustment vector; calculate a surface area of the sixthadjustment plane within an area bounded by the inner surface of theanatomical structure; select one of the third vector, the fifthadjustment vector, and the sixth adjustment vector in which the surfacearea is minimized; rotate the third vector in the yaw direction by thethird amount to define a seventh adjustment plane and a seventhadjustment vector; calculate a surface area of the seventh adjustmentplane within an area bounded by the inner surface of the anatomicalstructure; rotate the third vector in the yaw direction by the fourthamount to define an eighth adjustment plane and an eighth adjustmentvector; calculate a surface area of the eighth adjustment plane withinan area bounded by the inner surface of the anatomical structure; selectone of the third vector, the seventh adjustment vector, and the eighthsadjustment vector in which the surface area is minimized; determine anupdated second plane and an updated second vector based on the selectedone of the third vector, fifth adjustment vector, sixth adjustmentvector, seventh adjustment vector, and eighth adjustment vector; andidentify a location of the target treatment site based on the updatedfirst plane and updated second plane.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 shows a first exemplary medical system for identifying targettreatment locations;

FIG. 2 shows a second exemplary medical system for identifying targettreatment locations;

FIG. 3 shows an exemplary display of a segmented image of a left atriumof a heart, with coordinates of initial pulmonary vein locations;

FIG. 4 shows a geometrical representation of a method of determining asurface area of an intersection of a plane abc and an endocardialsurface;

FIG. 5 shows a geometrical representation of vector directions relativeto a pulmonary vein;

FIG. 6 shows a geometrical representation of a vector relative to acentroid of a first pulmonary vein contour;

FIG. 7 shows a geometrical representation of determining a centroid of asecond pulmonary vein contour;

FIG. 8 shows a geometrical representation of a method of determining aplurality of centroids along a length of a pulmonary vein;

FIG. 9 shows an exemplary display of a portion of a left atrium withrecommended target zones identified;

FIG. 10 shows a geometrical representation of a method of determiningtissue thickness; and

FIGS. 11A-11C show a flow chart of a method for identifying a targettissue location and thickness.

DETAILED DESCRIPTION

The method and system disclosed herein allows automatic location of atarget treatment structure, such as a pulmonary vein ostium, from ananatomical image. The method includes calculating a most likely path ofblood flow through a pulmonary vein based on a cross-sectional areaminimization technique and calculating pulmonary vein geometry as afunction of length. For example, a pulmonary vein ostium may be locatedby analyzing a change in pulmonary vein dimensional size or otheranatomical factors, such as absolute size. The method may also includedetermining tissue thickness at the pulmonary vein ostium or othertreatment size for treatment dose optimization. The method may be analgorithm performed by a processing unit of a navigation system or othercomponent of a medical system.

Before describing in detail exemplary embodiments that are in accordancewith the disclosure, it is noted that components have been representedwhere appropriate by conventional symbols in drawings, showing onlythose specific details that are pertinent to understanding theembodiments of the disclosure so as not to obscure the disclosure withdetails that will be readily apparent to those of ordinary skill in theart having the benefit of the description herein.

As used herein, relational terms, such as “first,” “second,” “top” and“bottom,” and the like, may be used solely to distinguish one entity orelement from another entity or element without necessarily requiring orimplying any physical or logical relationship or order between suchentities or elements. The terminology used herein is for the purpose ofdescribing particular embodiments only and is not intended to belimiting of the concepts described herein. As used herein, the singularforms “a”, “an” and “the” are intended to include the plural forms aswell, unless the context clearly indicates otherwise. It will be furtherunderstood that the terms “comprises,” “comprising,” “includes” and/or“including” when used herein, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

In embodiments described herein, the joining term, “in communicationwith” and the like, may be used to indicate electrical or datacommunication, which may be accomplished by physical contact, induction,electromagnetic radiation, radio signaling, infrared signaling oroptical signaling, for example. One having ordinary skill in the artwill appreciate that multiple components may interoperate andmodifications and variations are possible of achieving the electricaland data communication.

Referring now to the drawing figures in which like referencedesignations refer to like elements, an embodiment of a medical systemconstructed in accordance with the principles of the present inventionis shown in FIGS. 1 and 2, generally designated as “10.” In its simplestform, the system 10 includes a navigation system 12, although the system10 may also include a control unit 14 or operating console and a medicaldevice 16 in communication with the navigation system 12 and the controlunit 14. The system 10 may further include an imaging system 18 forobtaining images of anatomical features within a patient.

The medical device 16 may be a treatment and/or mapping device. Themedical device 16 may include an elongate body 22 passable through apatient's vasculature and/or proximate to a tissue region for diagnosisor treatment. For example, the device 16 may be a catheter that isdeliverable to the tissue region via a sheath or intravascularintroducer (not shown). The elongate body 22 may define a proximalportion 26, a distal portion 28, and a longitudinal axis 30, and mayfurther include one or more lumens disposed within the elongate body 22thereby providing mechanical, electrical, and/or fluid communicationbetween the elongate body proximal portion 26 and the elongate distalportion 28.

The medical device 16 may further include one or more treatment elements34 at, coupled to, or on the elongate body distal portion 28 forenergetic, therapeutic, and/or investigatory interaction between themedical device 16 and a treatment site or region. The treatment regionelement(s) 34 may deliver, for example, cryogenic therapy,radiofrequency energy, ultrasound energy, laser energy, or otherenergetic transfer with a tissue area in proximity to the treatmentelement(s), including cardiac tissue. For example, the treatmentelement(s) 34 may include thermally transmissive regions in thermalcommunication with a coolant or heat source, thermally transmissiveregions in electrically communication with a power source, surfacetherapeutic elements such as surface radiofrequency electrodes, or thelike. Additionally, the device 16 may include more than one type oftreatment element 34. In the exemplary system shown in FIG. 1, thedevice 16 may include a treatment element 34 that is expandable, such asone or more balloons. The expandable treatment element 34 may be coupledto a portion of the elongate body distal portion 28. The device 16 mayoptionally include a shaft 36 that includes a guidewire lumen and isslidably disposed within the elongate body 22 and at least a portion ofthe shaft 36 may be located within the expandable treatment element 34.The shaft 36 may further include or define a distal tip 38 that mayprotrude beyond the distal end of the expandable treatment element 34,and which may define an aperture in communication with the guidewirelumen. The expandable treatment element 34 may further include one ormore material layers providing for puncture resistance, radiopacity, orthe like. If the device 16 is used to delivery cryotherapy (or if usedwith another energy modality that requires fluid to be delivered to theinner chamber of the treatment element 34), the device may also includeone or more fluid injection elements. The device 16 may also include oneor more treatment elements in communication with a power source, such asone or more electrodes in communication with a source or radiofrequencyenergy. Further, if the device 16 is used or mapping in addition to orinstead of for the delivery of treatment, the device 16 may include oneor more mapping electrodes 40. Although the term “treatment element” isused herein, it will be understood that a mapping element or mappingelectrodes could be used instead.

Alternatively, the device 16 may include one or more treatment elementsthat are not expandable. For example, the device 16 may be a focalcatheter that includes one or more electrodes on the distal portion, ormay be a device that includes at least one carrier arm bearing one ormore treatment electrodes 34 (as shown in the exemplary system of FIG.2). Each treatment electrode 34 may be considered to be a treatmentelement. A device having a non-expandable treatment element may alsoinclude one or more fluid injection elements within the elongate body 18proximate the one or more treatment elements (for example, treatmentelectrode(s)). The device 16 shown in FIG. 2 may include one or morecarrier arms 44 that are coupled to a shaft 46 and are transitionablebetween a first configuration in with each carrier arm 44 is in an atleast substantially linear configuration and a second configuration inwhich each carrier arm 44 is in an expanded configuration.

The device 16 may also include one or more mapping electrodes 40 thatare used by the navigation system 12 to visualize the device 16 on acontrol unit display and/or a navigation system display. For example,the device 16 shown in FIG. 1 may include a first mapping electrode 40 adistal to the expandable portion of the treatment element 34 and asecond mapping electrode 40 b proximal to the expandable portion of thetreatment element 34. Although the mapping electrodes 40 a, 40 b areshown as being coupled to the portion of the treatment element 34 thatis coupled to the elongate body and/or shaft of the device, the mappingelectrodes 40 a, 40 b could alternatively be located distal and proximalto all portions of the treatment element, at any location on the device.

Each mapping electrode 40 and treatment element 34 in communication witha power source may be electrically conductive segments for conveying anelectrical signal, current, or voltage to a designated tissue regionand/or for measuring, recording, receiving, receiving, assessing, orotherwise using one or more electrical properties or characteristics ofsurrounding tissue or other electrodes. The electrodes may be configuredin a myriad of different geometric configurations or controllablydeployable shapes, and may also vary in number to suit a particularapplication, targeted tissue structure or physiological feature.

Although not shown, the system 10 may include one or more sensors tomonitor the operating parameters throughout the system, including forexample, pressure, temperature, flow rates, volume, power delivery,impedance, or the like in the control unit 14 and/or the medical device16, in addition to monitoring, recording or otherwise conveyingmeasurements or conditions within the medical device 16 or the ambientenvironment at the distal portion of the medical device 16. Thesensor(s) may be in communication with the control unit 14 forinitiating or triggering one or more alerts or therapeutic deliverymodifications during operation of the medical device 16. One or morevalves, controllers, or the like may be in communication with thesensor(s) to provide for the controlled dispersion or circulation offluid through the lumens/fluid paths of the medical device 16. Suchvalves, controllers, or the like may be located in a portion of themedical device 16 and/or in the control unit 14.

The medical device 12 may include a handle 50 coupled to the elongatebody proximal portion 26. The handle 50 may include circuitry foridentification and/or use in controlling of the medical device 16 oranother component of the system. Additionally, the handle 50 may alsoinclude connectors that are mateable to the control unit 14 to establishcommunication between the medical device 16 and one or more componentsor portions of the control unit 14. The handle 50 may also include oneor more actuation or control features that allow a user to control,deflect, steer, or otherwise manipulate a distal portion of the medicaldevice 16 from the proximal portion of the medical device 16. Forexample, the handle 50 may include one or more components such as alever or knob for manipulating the elongate body 22 and/or additionalcomponents of the medical device 16.

As used herein, the term “control unit 14” for simplicity may includeany system components that are not part of the medical device 16 itself,other than components of the navigation system 12 and the imaging system18, regardless of whether the component is physically located within orexternal to the control unit 14. Further, the navigation system 12 maybe a standalone system in communication with the control unit 14 or maybe contained within or integrated with the control unit 14, even thoughit is shown as being physically separated from the control unit in FIGS.1 and 2. The control unit 14 may include one or more components for thedelivery of one or more energy modalities for which the system is used.For example, if the system 10 is used to deliver cryotherapy, thecontrol unit 14 may include a supply 54 of a fluid such as a coolant,cryogenic refrigerant, or the like, an exhaust or scavenging system forrecovering or venting expended fluid for re-use or disposal, as well asvarious control mechanisms. In addition to providing an exhaust functionfor the fluid or coolant supply 54, the control unit 14 may also includepumps, valves, controllers or the like to recover and/or re-circulatefluid delivered to the handle 50, the elongate body 20, and/or the fluidpathways of the medical device 16. Further, a vacuum pump 56 in thecontrol unit 14 may create a low-pressure environment in one or moreconduits within the medical device 16 so that fluid is drawn into theconduit(s)/lumen(s) of the elongate body 22, away from the distalportion 28 and towards the proximal portion 26 of the elongate body 22.Additionally or alternatively, the control 14 unit may include an energysource 60 as a treatment or diagnostic mechanism in communication withthe treatment element(s) 34 of the medical device 16. The energy source60 may be a radiofrequency generator having a plurality of outputchannels, with each channel coupled to an individual treatment electrode34. The radiofrequency generator 60 may be operable in one or more modesof operation.

The control unit 14 may include one or more controllers, processors,and/or software modules 64 containing processing circuitry configured toexecute instructions or algorithms to provide for the automatedoperation and performance of the features, sequences, calculations, orprocedures described herein and/or required for a given medicalprocedure. Further, the control unit 14 may include one or more userinput devices, controllers, and displays 66 for collecting and conveyinginformation from and to the user.

The navigation system 12 may be any commercially available navigationsystem suitable for use with the control unit 14, device 16, and type ofprocedure. As a non-limiting example, the navigation system 12 mayinclude a plurality of navigation electrodes 70, a reference electrode(not shown), and a processing unit 72 that collects and processessignals from the device mapping electrodes 40, and a display 76 thatdisplays to the user the location of the device 12 within the patient'sbody 78 and/or relative to the target anatomical feature (for example, apulmonary vein ostium), recommended treatment areas, tissue thickness,or the like. The processing unit 72 may include processing circuitryincluding a memory and a processor, the memory in communication with theprocessor and having instructions that, when executed by the processor,configure the processor to perform the calculations and determinationsdiscussed herein. Additionally or alternatively, this information may bedisplayed on the display 66 of the control unit 14. The navigationsystem 12 may also include an energy source (not shown) for deliveringenergy to the plurality of navigation electrodes 70. Alternatively, thenavigation system 12 may be in communication with the control unitenergy source 60. For example, the processing unit 72 may be configured,programmed, or programmable to perform the calculations and make thedeterminations discussed in greater detail below to identify ananatomical feature and/or a target location for a medical device.Further, the processing unit 72 may execute software and display asoftware interface 80 with which the user may interact to make aselection, rotate and flag an image, open folders, control thenavigation system 12, or the like. As a non-limiting example, the usermay interact with the software interface 80 using a touch screen, akeyboard, a mouse, or other input device.

It will be understood that although the navigation system processingunit 72 is disclosed herein as performing the calculations discussedherein, it will be understood that the calculations may additionally oralternatively be performed by one or more processors 64 within thecontrol unit 14.

As shown in FIGS. 1 and 2, the navigation electrodes 70, which may alsobe referred to as surface electrodes, may be applied to the patient'sskin and may deliver relatively low-frequency radiofrequency energythrough the patient toward the procedure site, current device location,or the target anatomical feature. The mapping electrode 40 on the device16 may each record a voltage and impedance from this energy and transmitdata to the processing unit 72, which may then determine a position ofthe mapping electrode 40, and therefore the device 12, within thepatient. In addition to impedance-based systems, other navigationelectrodes may be used such as magnetic field based, hybridimpedance/magnetic field based, ultrasound field based, and/or radiationbased, and/or navigation systems that may be developed in the future.

The processing unit 72 may perform this calculation many times during aprocedure, frequently updating the registered location and displayingsuch to the user so the user can visualize the location of the devicerelative to the target anatomical feature in real time.

The imaging system 18 may be a computed tomography (CT) system, amagnetic resonance imaging (MRI) system, or other system suitable forcreating images of locations within a patient's body. For example, theimaging system may create images in Digital Imaging and Communicationsin Medicine (DICOM) format. The imaging system 18 may be incommunication with and digitally transmit images to the navigationsystem 12 and/or the control unit 14 for further processing.Alternatively, images recorded by the imaging system 18 may be recordedand transferred to the navigation system 12 and/or the control unit 14by a user.

FIGS. 3-10 will now be discussed with reference to the method flowchartshown in FIGS. 11A-11C. The method shown in the flow chart of FIGS.11A-11C is specific for determining an ostium of a left superiorpulmonary vein for purposes of example, but it will be understood thatthe method disclosed herein may be used to locate target treatmentlocations in other areas of the patient's body. As non-limitingexamples, the method may be used for structures such as the inferior orsuperior vena cava, the coronary sinus of the right atrium, and othernon-cardiac structures. Further, the method may be used to at leastsubstantially tubular anatomical structures, or those structures havinga lumen or plenum. Additionally, it will be understood that the elementsof FIGS. 3-10 are not drawn to scale and are meant only to show thegeometric relationship between components used to locate a targettreatment site.

Referring now to FIG. 3, a simplified segmented image of a left atriumof a heart is shown. The navigation system 12 may obtain a digitalanatomical image from the imaging system 18 (Step 1 in FIG. 11A). Thenavigation system 12 may be configured to at least temporarily store andprocess the anatomical image. Transmission may be wireless, through awired connection, from a portable data storage device, or the like.FIGS. 1 and 2 show the imaging system 18 as being in communication withthe control unit 14 and navigation system 12, but it will be understoodthat wired connections are optional. The processing unit 72 may thensegment the various structures within the digital anatomical imagereceived from the imaging system 18 to identify epicardial andendocardial surfaces of the anatomical feature (Step 2 in FIG. 11A). Forexample, a segmented image 82 of the left atrium 84 is shown in FIG. 3,although the image may be of any portion of the patient's body. Thesegmented anatomical image 82, and, optionally, the original anatomicalimage, may be displayed on the navigation system display 76 and/or thecontrol unit display 66, and the user may be able to interact with theimage 82 using the software interface 80. Although the segmentedanatomical image 82 shown in FIG. 3 is shown as a line drawing, it willbe understood that the segmentation of the anatomical image may also bea three-dimensional image. The left atrium (LA) 84 may include a rightsuperior pulmonary vein (RSPV) 86, a right inferior pulmonary vein(RIPV) 88, a left superior pulmonary vein (LSPV) 90, a left inferiorpulmonary vein (LIPV) 92, and a mitral valve 94. In addition, somepeople have atypical anatomies so additional pulmonary veins, or commonpulmonary veins, may be encountered, or some pulmonary veins or otheranatomical structures may be missing.

The user may select initial target positions on the segmented image 82using the software interface 80 (Step 3 in FIG. 11A). As a non-limitingexample, the user may select the initial positions 100 of the rightsuperior pulmonary vein (RSPV) 86, the right inferior pulmonary vein(RIPV) 88, the left superior pulmonary vein (LSPV) 90, and the leftinferior pulmonary vein (LIPV) 92. As shown in FIG. 3, an initialposition 100 within the RSPV may be represented by the coordinates(x_(RS), y_(RS), z_(RS)), an initial position 100 within the RIPV may berepresented by the coordinates (x_(RI), y_(RI), z_(RI)), an initialposition 100 within the LSPV may be represented by the coordinates(x_(LS), y_(LS), z_(LS)), and an initial position 100 within the LIPVmay be represented by the coordinates (x_(LI), y_(LI), z_(LI)).Reference made herein to coordinates may be to coordinates in athree-dimensional space as defined by the surface electrodes 70 of thenavigation system 12 or other reference points in the structure definedby the navigation system.

The processing unit 72 may then calculate a centerpoint 102 within theLA 84 represented by the coordinates (x_(C), y_(C), z_(C)) (Step 4 inFIG. 11A). The centerpoint 102 may be equidistant from the initialpositions 100 within the RSPV, RIPV, LSPV, and LIPV. The processing unit72 may calculate the centerpoint 102 according to the followingequation:(x _(C) ,y _(C) ,z _(C))=[¼(x _(RS) +x _(RI) +x _(LS) +x _(LI)),¼(y_(RS) +y _(RI) +y _(LS) +y _(LI)),¼(z _(RS) +z _(RI) +z _(LS) +z_(LI))]  (1)

The user may then select a first or initial anatomical location usingthe software interface 80 (Step 5 of FIG. 11A). Alternatively, theprocessing unit 72 may automatically choose the first location. Forexample, a location within a pulmonary vein may be chosen. A firstlocation within each pulmonary vein may be selected in any order, butfor illustration the first location within the LSPV may be selected. Theprocessing unit 72 may then define or set an initial guess of the LSPVcenter 104 coordinates as:(x ₀ ,y ₀ ,z ₀)=(x _(LS) ,y _(LS) ,z _(LS))  (2)and may then estimate a plane abc 108 that defines the direction ofblood flow within the LSPV as:a(x−x ₀)+b(y−y ₀)+c(z−z ₀)=0  (3)where

a, b, c

is a vector {right arrow over (v)}₀ normal to the plane abc 108, withthe initial guess of the LSPV center 104 being:

a,b,c

=

(x _(C) −x ₀),(y _(C) −y ₀),(z _(C) −z ₀)

  (4)As the LSPV is at least substantially tubular (that is, defines alumen), the LSPV center (x₀, y₀, z₀) is located within the LSPV lumenand not on a portion of tissue. The plane abc 108 may span or extendacross the lumen or a cross-sectional area of the LSPV (90), as shown inFIG. 4. As blood flows through the pulmonary veins toward the LA, thevector

a, b, c

may extend from LSPV center (x₀, y₀, z₀) toward the LA. Thus, at thisstage in the method, vector

a, b, c

may represent an initial estimated direction of blood flow through theLA. In the next steps, vector

a, b, c

is further defined such that vector

a, b, c

defines a plane that has a minimum surface area when measured by theboundary where the plane intersects the anatomical feature (defined bycontour S_(n)). For example, the methods described below in Steps 6-15are one possible approach for determining the direction of flowcorresponding to the direction when the plane abc and the anatomicalcontour S_(n) comprise a minimum cross-sectional area of the anatomicalfeature. However, it will be understood that other mathematicalalgorithms could additionally or alternatively be used to determine thedirection of flow, and the methods described in Steps 6-15 may not bethe only way to do so.

The processing unit 72 may then identify a vector

d, e, f

lying in plane abc 108 (Step 6 in FIG. 11A). The vector

d, e, f

may be normal to

a, b, c

, as

a, b, c

is normal to plane abc 108. The vector

d, e, f

may be determined by introducing a slight perturbation in two of thedirections and calculating the third. For example, the processing unit72 may select the two directions having the smallest magnituderepresented by

a, b, c

such that {circumflex over (x)} and ŷ are selected if c>a, c>b. Forexample, small perturbations may be selected around (x₀, y₀, z₀) in theselected directions as in (x₀+Δx, y₀+Δy, z₀). Given the plane abc 108and new points x₀+Δx and y₀+Δy, the processing unit 72 may calculate Δzsuch that the following expression is satisfied:

$\begin{matrix}{{\frac{{- {a\left( {x_{0} + {\Delta\; x}} \right)}} - {b\left( {y_{0} + {\Delta\; y}} \right)}}{c} - z_{0}} = {\Delta\; z}} & (5)\end{matrix}$

The vector created by the new point (Δx, Δy, Δz) may lie in the planeabc and be perpendicular to the normal vector

a, b, c

with a resulting vector

d, e, f

described as:

d,e,f

=(x ₀ ,y ₀ ,z ₀)+t(Δx,Δy,Δz)  (6)

Starting at (x₀, y₀, z₀), the processing unit 72 may then increase tuntil the vector

d, e, f

intersects the endocardial surface S_(n) (for example, an inner wall ofthe LSPV) (Step 7 in FIG. 11A). The processing unit 72 may record thisdistance (r_(i))_(C) between the new starting point (Δx, Δy, Δz) and theendocardial surface S_(n).

Referring now to FIG. 4, the processing unit 72 may then rotate thevector

d, e, f

around the vector

a, b, c

by a small degree θ (Step 8 of FIG. 11A). The degree θ may be fixed oradaptive. The rotation may be calculated according to the followingequation (Rodrigues's formula):{right arrow over (V)} _(rot) ={right arrow over (V)} cos θ+({rightarrow over (k)}×{right arrow over (v)})sin θ+{right arrow over(k)}({right arrow over (k)}×{right arrow over (v)})(1−cos θ)  (7)where:{right arrow over (v)}=

d, e, f

and {right arrow over (k)}=

a, b, c

and {right arrow over (V)}_(rot) is the new rotated vector.

The processing unit 72 may repeat this calculation of (r_(i))_(C) inthis rotated vector {right arrow over (V)}_(rot) in the new directionfrom the point (x₀, y₀, z₀) (Step 9 in FIG. 11B).

When θ has been spanned by 2π radians, or 360°, the processing unit 72may calculate the surface area A of an area defined by the intersectionof plane abc 108 and the endocardial surface S_(n) according to thefollowing equation (Step 10 in FIG. 11B):

$\begin{matrix}{A = {\sum\limits_{i = 1}^{n}{r_{i}\frac{\theta_{i + 1} - \theta_{i - 1}}{2}}}} & (8)\end{matrix}$where n is the number of angular sweeps performed by the processing unit72 in executing the algorithm and 0≤θ_(i)≤2π. The surface area A of anarea defined by the intersection of plane abc 108 and the endocardialsurface of the pulmonary vein. So, performing this calculation mayindicate the shape of the lumen of the pulmonary vein, which may bereferred to as the contour, and the cross-sectional size of thepulmonary vein lumen.

Referring now to FIG. 5, the processing unit 72 may update the initialguess for the LSPV center (x₀, y₀, z₀), and therefore an initial guessfor the flow direction vector

a, b, c

by perturbing the vector in two orthogonal directions (Step 11 in FIG.11). The first orthogonal direction may be referred to as the pitchdirection {right arrow over (v)}_(p) and the second orthogonal directionmay be referred to as the yaw direction {right arrow over (v)}_(y). Boththe pitch and yaw directions may lie in the plane abc and also beorthogonal to each other. The pitch direction may be chosen as theinitial vector

d, e, f

calculated previously in the Step 6 of the method. The yaw direction canthen be calculated by taking the cross product according to thefollowing equation, or by another equivalent method:

a,b,c

×

d,e,f

=

m,n,p

  (9)This new vector

m, n, p

lies in the plane abc and is perpendicular to both

a, b, c

and

d, e, f

.

The processing unit 72 may rotate vector

a, b, c

in the pitch direction by an amount +θ_(p) using equation (7) (Step 12in FIG. 11). This calculation may define a new adjustment plane(abc)^(i+1) and first adjustment vector

a, b, c

^(i+1). The processing unit may repeat the calculation described above,or an equivalent method, to calculate a new area of the adjustment plane(abc)^(i+1) intersecting the endocardial surface S_(n). The processingunit 72 may then rotate vector

a, b, c

in the pitch direction by −θ_(p) using equation (7) to define a secondadjustment plane (abc)^(i−1) and second adjustment vector

a, b, c

^(i−1). The processing unit 72 may then calculate a new area of thesecond adjustment plane (abc)^(i+1) intersecting the endocardial surfaceS_(n), as discussed above. The processing unit 72 may then select thefirst updated vector

a, b, c

from the adjustment vectors

a, b, c

^(i) (the original vector

a, b, c

),

a, b, c

^(i+1), and

a, b, c

^(i−1) where the surface area A is minimized (i.e., where the surfacearea A is smallest). The direction corresponding to the minimum surfacearea is an estimate for the most likely directly of flow at that pointin the anatomical structure.

The processing unit 72 may rotate the updated vector

a, b, c

according to equation (7) around the yaw direction by an amount of+φ_(y) and −φ_(y) to determine vector

a, b, c

^(j+1) and vector

a, b, c

^(j−1), respectively (Step 13 in FIG. 11). The processing unit 72 maythen calculate the surface areas A^(j+1) and A^(j−1) in the methoddescribed above with the yaw-adjusted planes and the endocardial surfaceS_(n). The processing unit 72 may then select the second updated vector

a, b, c

from vectors

a, b, c

^(j),

a, b, c

^(j+1), and

a, b, c

^(j−1) where the surface area A is minimized.

The processing unit 72 may repeat Steps 12 and 13 iteratively until thesurface area A is minimized (Step 14 in FIG. 11). The updated vector

a, b, c

′ may now be normal to the plane 108′ that is perpendicular to the mostlikely direction of blood flow, the plane being defined as follows:ax+by+cz+d=0  (10)Plane a, b, c 108 and original vector

a, b, c

represented an estimated direction of blood flow through the LSPV. Atthis stage in the method, however, the direction of blood flow may bemore certain and plane a, b, c may be adjusted slightly (the adjustedplane being represented as 108′ in FIGS. 5 and 6), meaning that vector

a, b, c

may also be adjusted slightly (the adjusted or updated vector beingrepresented as

a, b, c

′ in FIGS. 5 and 6).

Referring now to FIG. 6, the area defined by the contour C, the boundaryof the inner surface of the LSPV where intersected by plane abc, may nowbe defined (Step 15 of FIG. 11). The processing unit 72 may thencalculate the centroid 110 of the plane abc 108′ constrained by C. Asthe plane abc 108′ constrained by C may not be a perfect circle, thispoint is referred to as a centroid rather than a center point.Calculation of the centroid 110 may provide updated coordinates for theinitial center guess (x₀, y₀, z₀) for the LSPV (90).

Referring now to FIG. 7, the processing unit 72 may determine a startingpoint 110 a (x₁, y₁, z₁) for the next calculation (Step 16 in FIG. 11).The starting point 110 a (x₁, y₁, z₁) may be a predetermined or adaptivedistance in the direction of vector

a, b, c

′a, the coordinates of the location being calculated by the followingequation:(x ₁ ,y ₁ ,z ₁)=(x ₀ ,y ₀ ,z ₀)+t

a,b,c

  (11)where t indicates a physical distance from x₀, y₀, z₀ along the vector

a, b, c

.

The processing unit 72 may repeat Steps 6 through 16 using the newlocation 110 a (x₁, y₁, z₁) as the initial guess of the LSPV center(Step 17 in FIG. 11). These steps may also be repeated a plurality oftimes using the location coordinates of the previous repetition (x_(n),y_(n), z_(n)) as the initial guess of the LSPV center. For example, FIG.8 shows location 110 a being defined from location 100 along vector

a, b, c

′a using coordinates (x₁, y₁, z₁), a new location 110 b being definedfrom location 110 a along vector

a, b, c

′b using coordinates (x₂, y₂, z₂), new location 110 c being defined fromlocation 110 b along vector

a, b, c

′c using coordinates (x₃, y₃, z₃), so on until n locations have beendefined.

Using this method, the processing unit 72 may calculate the direction ofblood flow in each pulmonary vein (Step 18 in FIG. 11). As shown in FIG.8, the supplemental vectors

a, b, c

′a-

a, b, c

′n determined from the new starting locations 110 a-110 n may togethershow an overall direction of blood flow throughout the pulmonary vein.

Further, the areas centered at each centroid point may be used by theprocessing unit 72 to estimate the cross-sectional area of the pulmonaryvein (Step 19 in FIG. 11). In other words, the processing unit 72 maycalculate the surface area A for each plane 108′a-108′n. These surfaceareas A may together indicate the overall anatomy of the LSPV (90).

Finally, the processing unit 72 may determine or estimate the ostium orother ablation target for each pulmonary vein (Step 20 in FIG. 11).These locations may be displayed on the navigation system display and/orthe treatment system display. As a non-limiting example, a pulmonaryvein ostium 114 may be indicated by the best guess contour based on thedetermined geometry and/or size of the pulmonary vein, a range ofprobably locations based on the size of the pulmonary vein, and/orchanges in size of the pulmonary vein over distance. For example, apulmonary vein may have an increasing inner diameter in the direction ofblood flow (i.e., toward the left atrium). Accordingly, the processingunit 72 may compare surface areas between pairs of adjacent planes toidentify a trend, such as a decreasing or increasing diameter over alength of the pulmonary vein. These features may also be considered inlight of the location of the centerpoint 102 in the left atrium 102, asthe centerpoint 102 may provide a reference for determining where theostium may be. The processing unit 72 may reference a table of pulmonaryvein measurement data to estimate the location of the ostium 114 basedon statistical probability using the features described immediatelyabove.

Additionally, the displayed anatomical features may also be used todetermine where a particular treatment device may be used, based on thegeometry of the treatment device and the anatomical feature. Forexample, using the methods described in U.S. Ser. No. 15/259,683, theentirety of which is incorporated herein by reference, one or moretarget “landing zones” for treatment elements or other parts of themedical device 16 may be determined and displayed to the user. Forexample, the processing unit 72 may determine a distal target site 116 aand a proximal target site 116 b to be used as navigation targets whenmaneuvering the device 16 to a treatment area.

The success of a treatment may depend on delivering the optimal dose oftreatment energy to the target tissue site, which may in turn depend ontissue thickness at the target tissue site. With the pulmonary veinostium 114 identified, the thickness of the pulmonary vein can bedetermined by calculating the distance between the endocardial surfacedS_(n), or inner pulmonary vein surface, and the epicardial surfacedS_(p), or outer pulmonary vein surface, along the pulmonary vein ostiumidentified using the method described above (Step 21 in FIG. 11). Tissuethickness T may be calculated in a plurality of directions from thecenter of contour C and perpendicular to the vector

a, b, c

using the following formula:T=dS _(p) −dS _(n)  (12)Further, the pulmonary vein contour C may be swept along pulmonary veinand the calculation made at every location, which may provide anestimate of tissue thickness along the length of the pulmonary vein andat the ostium 114. The calculated thicknesses may be used to determineoptimum treatment energy dose. As a non-limiting example, ifcryoablation is used, the control unit 14 may adjust the temperature ofthe treatment element(s) 34 and/or treatment time such that thickertissue is treated at a lower temperature and/or for a longer period oftime than thinner tissue.

As will be appreciated by one of skill in the art, certain conceptsdescribed herein may be embodied as a method, data processing system,and/or computer program product. Accordingly, these concepts describedherein may take the form of an entirely hardware embodiment, an entirelysoftware embodiment or an embodiment combining software and hardwareaspects. Furthermore, the disclosure may take the form of a computerprogram product on a tangible computer usable storage medium havingcomputer program code embodied in the medium that can be executed by acomputer. Any suitable tangible computer readable medium may be utilizedincluding hard disks, CD-ROMs, electronic storage devices, opticalstorage devices, or magnetic storage devices.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed herein above. In addition, unless mention was made above tothe contrary, it should be noted that all of the accompanying drawingsare not to scale. A variety of modifications and variations are possiblein light of the above teachings without departing from the scope andspirit of the invention, which is limited only by the following claims.

What is claimed is:
 1. A system for locating a target treatment site,the system comprising: a processing unit including a processingcircuitry including a memory and a processor, the memory incommunication with the processor and having instructions that, whenexecuted by the processor, configure the processor to: determine aplurality of planes, each of the plurality of planes having a center andextending across a cross-sectional area of an anatomical structure, theanatomical structure having a lumen, an inner surface, and an outersurface, the plurality of planes being over a length of the anatomicalstructure; determine a plurality of vectors, each of the plurality ofvectors extending from the center of a corresponding one of theplurality of planes; calculate a surface area of each of the pluralityof planes, the surface area being bounded by the inner surface of theanatomical structure; calculate a difference between surface areas ofeach pair of adjacent planes of the plurality of planes; identify atarget treatment site based at least in part on the calculateddifference, determine a thickness of an area of the anatomical structureby calculating a distance between the outer surface and the innersurface of the anatomical structure; and determine an optimal treatmentenergy dose for delivery at the target treatment site, the determinedoptimal treatment energy dose being based at least in part on thedetermined thickness.
 2. The system of claim 1, wherein the processingis further configured to: compare a direction of each of the pluralityof vectors, the identification of the target treatment site being basedat least in part on the comparison.
 3. The system of claim 1, whereinthe processor is configured to determine the plurality of planes basedon an anatomical image of the anatomical structure.
 4. The system ofclaim 3, wherein the anatomical image is a segmented image.
 5. Thesystem of claim 1, wherein the anatomical structure includes the targettreatment site.
 6. The system of claim 5, wherein the anatomicalstructure is a pulmonary vein and the target treatment site is an ostiumof the pulmonary vein.
 7. The system of claim 1, further comprising: anavigation system, the navigation system being configured to store ananatomical image of an area of tissue including the target treatmentsite.
 8. The system of claim 7, wherein the processing unit is part ofthe navigation system.
 9. The system of claim 7, further comprising: amedical device including at least one treatment element and at least onemapping electrode, the at least one mapping electrode being incommunication with the navigation system.
 10. The system of claim 9wherein the navigation system further includes: a display; and at leastone navigation electrode.
 11. The system of claim 10, wherein theprocessor is further configured to: determine a target position for themedical device; and displaying to a user the target position of themedical device on the display of the navigation system.
 12. The systemof claim 1, wherein each of the plurality of vectors is normal to thecorresponding one of the plurality of planes.
 13. The system of claim 1,wherein the processor is further configured to: determine a plurality ofdistances between the center of each of the plurality of planes and theinner surface of the anatomical structure.